A continuing goal in semiconductor processing is increased miniaturization while maintaining high performance. Modern semiconductor processes are still heavily reliant on photolithography when fabricating semiconductor circuitry to achieve this goal.
Photolithography is a commonly-used method for patterning features during semiconductor processing. A radiation-sensitive material (i.e., photoresist) is formed over a substrate which is ultimately to be patterned, for example by etching or ion implanting. The photoresist is subsequently subjected to radiation which modifies the solubility of the impacted versus the unimpacted regions in a suitable developer solution. Accordingly, the radiation is provided in a desired pattern so that some portions of the photoresist are impacted by the radiation while other portions of the photoresist are not impacted by the radiation. The photoresist is then subjected to developing conditions which selectively remove either the impacted or the non-impacted portions. Photoresists are typically designed to be either negative or positive. If the photoresist is a positive photoresist, the impacted portions are selectively removed. If the photoresist is a negative photoresist, the non-impacted portions are selectively removed.
The photoresist remaining after development defines a patterned mask. The pattern of such mask can subsequently be transferred to the underlying material using appropriate etching and/or implanting techniques to form patterned features in material beneath the mask. A difficulty which can be encountered during photolithographic processing is that the radiation utilized to pattern the photoresist can be reflected from the underlying layer or layers to cause various constructive and destructive interference patterns to occur. This can adversely affect the pattern ultimately developed in the photoresist.
One manner of addressing the reflective issues is to initially form an antireflective coating over the layer or layers to be patterned, and then forming a layer of photoresist thereover. Further, multiple antireflective coating materials or layers might be utilized, as well as multiple layers of resist and/or non-radiation sensitive hard masking or other layers. Various antireflective coating materials have been developed. Some are principally organic in nature, while others are principally inorganic in nature. DARC, which stands for Deposited Antireflective Coating, is typically understood within the industry to define inorganic antireflective coatings formed of silicon, oxygen, nitrogen and sometimes hydrogen. Another commonly used class of antireflective coating is BARC, which stands for Bottom Antireflective Coating. BARC materials are principally organic in nature.
The continuing goal and effect of circuitry miniaturization has typically resulted in greater reduction in the horizontal dimension as compared to the vertical dimension. In the etching of features, this has resulted in narrower yet correspondingly increasing height in the features being formed, something typically referred to as increasing aspect ratio. Correspondingly, the photoresist masks utilized to form such features typically also have increased aspect ratios. Accordingly, adherence of the photoresist to the underlying antireflective coating or other layers takes on increasing significance towards precluding displacement or toppling of the masking blocks formed in the patterned photoresist. Further and regardless, the photoresist and antireflective coating materials can interact, particularly during a post-exposure bake of the photoresist prior to solvent development. For example, material at the outer surface of the antireflective coating materials can migrate into the photoresist, and/or the photoresist can interact with material on the outer surface of the antireflective coating which can, one or both, adversely affect adherence or desired control in the ultimate pattern produced in the photoresist.
In most instances, it is highly desirable that the photoresist masking blocks which are formed have substantially vertical sidewalls from top to bottom of the photoresist layer. However, the patterned photoresist can tend to flare out at the bottom/bases of the individual masking blocks forming what is commonly referred to as footing. The degree of footing can be exacerbated by use of certain antireflective coatings, principally the result of interaction between the photoresist and outer surface of the antireflective coating. Further in some instances, the patterned photoresist can tend to recess in at the bottom/bases of the individual masking blocks which can lead to collapse/toppling of portions of the mask and/or less than desired transfer of the mask pattern to underlying layers.
While the invention was motivated in addressing the above-identified issues, it is in no way so limited. The invention is only limited by the accompanying claims as literally worded, without interpretative or other limiting reference to the specification, and in accordance with the doctrine of equivalents.